Method of making piping



Oct. 29, 1929. e. A. FERRAND METHOD OF MAKING PIPING Filed Oct. 11, 1927 Fig.1

Patented Oct. 29, 1929 UNITED STATES PATENT OFFICE GEORGES AUGUSTE FERRARI), OI GBENOBLE, FRANCE manner) or mxme rxrmc application filed October 11, 1927', Serial No. 225,566, and in August 8, 1825.

This invention relates to the construction of piping for systems intended to be subjected to heavy internal pressures, and in particular for installation 111 the pressure lines a of hydro-electric generating stations of high power and with high-head falls.

In plants of this character, the buildingoi'the largepressure pipe lines is generally the most/costly item and to reduce the ex- 11o pense, it has been proposed to split the total cross-sectional pipe area required into several fractions, using a separate pipe line for each. But while such expedient may aflord greater security and may insure increased flexibility it of working, it actually entails an exceedingly heavy additional expenditure because the cost of labor as regards both transport and erecting is doubled, and the .accesspry earth and masonry work is also greater.

The object of the present invention is to render possible the construction of pipe lines which could' not heretofore be built with the means usually at the disposal of the engineers, and to effect an appreciable saving as com- 25 pared with the ordinary installations. 'According to the invention, a steel tube is used to form the wall of the pipe, and on this wall steel hoops or rings are arranged at regular intervals, the tube or wall being slightly coreo rugated between each two successive hoops- The manner in which the hoo s are anchored on the tube constitutes one o the important features of the invention, as will be explained more fully hereinafter, as well as the relation- 8 shi between the hoops and corrugations and their function with respect to the finished Til the accompanying drawing, Figure 1 is a side elevation -of a pipe constructed in accordance with the invention, and Figs. 2 and 3 are, respectively, a transverse section and a fragmental lon 'tudinal section, both taken vertically throug Fig. 1., I

Referring more particularly to the drawing, 1 indicates the tube or wall previously mentioned, and 2 the rings or hoops thereon. Tube 1 is made of thin extra-mild steel in the usual manner-that is, it may be welded with water gas, or drawn without weldin etc.-'

5 and consists of a single ply or thi cos of such steel of indeterminate length. The hoops 2, on the other hand, are made of special extra-strong steel rolled in one piece without yielding.

These hoops are placed on the tube at the intervals determined by calculation, their diameters and that of the tube being chosen so that the hoo s fit cold on the tube and can easily be put t ereon without requiring the use of special (devices. Consequently, there will be a slight initial clearance between the hoops and the tube which should be reduced as much as possible. The hooped tube is then placed between the two plates of a hydrauhc testing press; and after the necessary tight joints have been made at its ends, it is gradually subjected to an internal pressure which is generally stopped when it reaches a point two and one-half times the normal working pressure; this maximum pressure being termed the binding pressure and being maintained for about five minutes.

Under the action of the increasing pressure, the tube or wall 1 becomes elongated, begins to press outwardly against the hoops,

and finally assumes the form of anarc between them, such arcs constituting the annu- -lar corrugations 3 of the finished pipe.

During this operation, the elastic limit of the sheet metal is exceeded, and the deformation of thewa'll is a permanent set or deformation. The finished pi e will have undergone a hydraulic test with anexcess 'of pressure of 150% relatively to the normal working ressure, as willbe understood from the oregoing, and it will thus have a definite and certain safety factor of 2.5 relatively to the elastic limit of the metal, no risk being present so long as the internal pressure does not. reach the binding pressure. The hoops themselves will be permanently locked or fixed in place with absolute rigidity, due to the formation of the corrugations 3, which project slightl beyond the hoops at opposite sides; and in the subsequent use of the finished pipe, the hoops thus afl'ord the main resistance to the internal pressure. In laying the pipes, the bends in the pipe lines are preferably anchored, but, contrary to what is usual, the use of expansion joints is unnecescally neghgible, for the ratio between the depth of the corrugations and the diameter of the pipe is so small that there will bevery little disturbance caused by the corrugations in the normal flow of liquid. However, should there be any fear of substantial head losses from the presence of the corrugations, a smooth liner of thin sheet metal can readily be arranged in the interior of the tube.

As further regards the so-called binding pressure mentioned above, it may be explained that if an originally homogeneous tube be subjected to increasing internal pressures, the elongation or extension in the successive layers, so to say, at first elastic, will vary in inverse ratioto the radii of the layers; such pressures, therefore, having their greatest value at the inner surface of the tube. Per- V manent deformations will be produced when the internal pressure reaches a sufficient value, the deformations taking place initially in the layers adjoining the inner surface and progressing towardthe outside as the pressure increases; and when a still higher pressure is attained, the ermanent elongation will extend to the ent re tube. These permanent ,deformations decrease, therefore, in relative value or degree from the interior toward the outside. 4

Hence, it follows that when the internal pressure is relieved and the tube is at'rest, it will be in a state of equilibrium such that each layer will tend to compress the one which is on its inner side and to be compressed b the one on its outer side, so that the effect 0 tained is that of a tube constituted by a series of thin concentric hoops forced into one another.

The present application is a continuation in part of my prior application for the same invention filed June 24, 1926 under Serial No. 118,266. Y

. I claim as my invention:

large diameter adapted to withstan high internal working pressures, comprisin the steps of arranging steel hoops on a tu e of thin sheet steel of indeterminate length at regular intervals .apart; subjecting the tube to a gradually-increasing internal pressure; and stopping such pressure when it reaches a point which is about two and one-half times the normal working pressure to which the pipe. issubjected when in use, thereby to form permanent transverse annular corrugations in the tube between successive hoops and to lock the "hoops rigidly in place betwen adjacent corrugations. i

1. A method of makingmetal pi es of,

which the maximum internal pressure of two and one-half times the normal working pressure is maintained for a eriod of about five minutes-before being re ieved.

In testimony whereof I afiix my signature, GEORGES AUGUS TE FERRAND.

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